Fabrication of Flexible and Transparent Conductive Nanosheets by the UV-Irradiation of Gold Nanoparticle Monolayers.

Conductive films that are highly transparent and flexible are extremely attractive for emerging optoelectronic applications. Currently, indium-doped tin oxide films are the most widely used transparent conductive films and much research effort is devoted to developing alternative transparent conductive materials to overcome their drawbacks. In this work, a novel and facile approach for fabricating transparent conductive Au nanosheets from Au nanoparticles (AuNPs) is proposed. Irradiating an AuNP monolayer at the air-water interface with UV light results in a nanosheet with ≈3.5 nm thickness and ≈80% transparency in the UV-visible region. Further, the so-fabricated nanosheets are highly flexible and can maintain their electrical conductivity even when they are bent to a radius of curvature of 0.6 mm. Fourier-transform infrared and X-ray photoelectron spectroscopy characterizations reveal that the transformation of the monolayer of AuNPs into the nanosheet is induced by the photodecomposition and/or photodetachment of the dodecanethiol ligands capping the AuNPs. Further, the UV-irradiation of a hybrid monolayer consisting of AuNPs and silica particles affords the patterning of Au nanosheets with periodic hole arrays.

Conditioned Medium From Mesenchymal Stem Cells Enhances Early Bone Regeneration After Maxillary Sinus Floor Elevation in Rabbits.

PURPOSE: Conditioned medium from stem cells contains growth factors and has a promising prospect for use in regenerative medicine. In this study, the effects of marrow-derived stem cell-conditioned medium (MSC-CM) on bone regeneration after maxillary sinus floor elevation were examined in rabbits. MATERIALS AND METHODS: Rabbit bone marrow-derived stem cells (rMSCs) were cultured with MSC-CM for 48 hours, and their mobilization and proliferation were evaluated. Beta-tricalcium phosphate scaffolds were impregnated with MSC-CM and grafted in the rabbit maxillary sinus cavities. At 2, 4, and 8 weeks after transplantation, sections of the newly formed bone were evaluated histologically and by immunohistochemical staining. RESULTS: MSC-CM increased the migration and proliferation of rMSCs and the early bone regeneration in rabbit sinus. Cell proliferation and vascularization were increased at 2 weeks after implantation of grafts impregnated with MSC-CM compared to controls, indicating that MSC-CM is effective at the early phase of bone regeneration. CONCLUSION: MSC-CM is a promising novel therapeutic agent to promote bone regeneration after maxillary sinus floor elevation.

Effects of the permeability of shields with autologous bone grafts on bone augmentation.

PURPOSE: The objective of this study was to histologically evaluate and compare the effects of the permeability of shields on bone augmentation in a rabbit calvarial model. MATERIALS AND METHODS: Twelve adult male Japanese white rabbits were used for the study. Each received four titanium cylinders, which were placed into perforated slits made in the outer cortical bone of the calvaria and filled with autologous iliac bone. The tops of the cylinders were randomly covered with the following test materials: (1) uncovered (control), (2) a titanium mesh, (3) an expanded polytetrafluoroethylene (e-PTFE) membrane, or (4) a titanium plate. After 8 weeks, the animals were sacrificed, and ground sections were obtained for histomorphometric analysis. RESULTS: There was no significant difference in augmented bone volume among all groups. However, the distribution of augmented bone in the cylinders differed among the groups. In the uncovered control, there was significantly less augmented bone in the upper third of the cylinder than in the middle or lower thirds. Findings were similar for the titanium mesh group and the e-PTFE membrane group, with significantly less augmented bone in the upper third than in the middle or lower thirds. In the titanium plate group, there was no significant difference in augmented bone among the upper, middle, and lower thirds. The differences among the upper, middle, and lower thirds of the cylinder were smaller in the order of titanium plate, e-PTFE membrane, titanium mesh, and uncovered control. CONCLUSION: The use of low-permeability shields resulted in small differences in the distribution of bone structure in the present bone augmentation model.

Effects of implant surface on bone healing around titanium screw implants in ovariectomized rats.

PURPOSE: The aim of this study was to investigate whether estrogen deficiency interrupts bone healing around titanium implants and to evaluate whether bone healing around implants under a condition of estrogen deficiency is affected by variations in implant surface characteristics. MATERIALS AND METHODS: Forty-eight female rats were divided into two groups: ovariectomized rats (OVX; n = 24) and sham-operated rats (SHAM; n = 24). Each group was further divided into two groups: a machine-polished implants group and a sandblasted implants group. One implant was placed into the left femur of each rat 84 days after OVX or sham surgery. After 28 or 56 days, the rats were killed, and nondecalcified sections were obtained. Bone-to-implant contact (BIC) and bone area (BA) around the implants were assessed for cortical and cancellous bone. Furthermore, bone density (BD) was evaluated in a 500-mm-wide zone of cancellous bone lateral to the implants. RESULTS: At 28 and 56 days after implantation, no significant differences were found between the OVX and SHAM groups for BIC and BA in cortical bone. BIC, BA, and BD with cancellous bone were lower in the OVX group than in the SHAM group. However, BIC and BA tended to increase with the sandblasted implant surface. CONCLUSIONS: Estrogen deficiency affected bone healing and bone density around titanium implants, especially in cancellous bone, but the sandblasted surface has the possibility to improve osseointegration. However, the positive effect of this rough surface is limited at the implant surface.

Effects of self-assembling peptide hydrogel scaffold on bone regeneration with recombinant human bone morphogenetic protein-2.

PURPOSE: The objective of this pilot study was to histologically evaluate bone regeneration using a self-assembling peptide hydrogel scaffold with recombinant human bone morphogenetic protein-2 (rhBMP-2) in a rabbit calvaria model. MATERIALS AND METHODS: Five adult New Zealand White rabbits were used for the study. Each received four titanium cylinders, which were placed into perforated slits made in the outer cortical bone of the calvaria. The cylinders were filled with the following test materials: (1) unfilled control; (2) rhBMP-2; (3) PuraMatrix (PM), a synthetic self-assembling peptide (RADA16-I) consisting of a 16-amino acid sequence and with a three-dimensional structure; and (4) PM/rhBMP-2. Each cylinder was covered with a titanium lid. After 8 weeks, the animals were sacrificed, and ground sections were obtained for histomorphometric analysis. RESULTS: Histomorphometric analysis showed that regenerated tissue in the cylinder with PM/rhBMP-2 was significantly increased compared to the empty control. The mean area values of regenerated tissue in the cylinders were 35.80% ± 10.35% (control), 47.94% ± 5.65% (rhBMP-2), 48.94% ± 11.33% (PM), and 58.06% ± 14.84% (PM/rhBMP-2). The mean area values of newly formed bone in the cylinders were 9.39% ± 4.34% (control), 14.03% ± 2.25% (rhBMP-2), 13.99% ± 2.15% (PM), and 16.61% ± 3.79% (PM/rhBMP-2). Neither rhBMP-2 nor PM alone significantly enhanced bone regeneration compared to the empty control cylinder. CONCLUSIONS: PM with rhBMP-2 significantly enhanced bone regeneration on the bone augmentation model in a rabbit. PM promises to be a useful alternative synthetic material as a carrier for rhBMP-2 for bone regeneration.

Stromal cell-derived factor-1 enhances distraction osteogenesis-mediated skeletal tissue regeneration through the recruitment of endothelial precursors.

Distraction osteogenesis (DO) is a unique therapy that induces skeletal tissue regeneration without stem/progenitor cell transplantation. Although the self-regeneration property of DO provides many clinical benefits, the long treatment period required is a major drawback. A high-speed DO mouse model (H-DO), in which the distraction was done two times faster than in control DO (C-DO) mice, failed to generate new bone callus in the DO gap. We found that this was caused by the unsuccessful recruitment of bone marrow endothelial cells (BM-ECs)/endothelial progenitor cells (EPCs) into the gap. We then tested the ability of a local application of stromal cell-derived factor-1 (SDF-1), a major chemo-attractant for BM-ECs/EPCs, to accelerate the bone regeneration in H-DO. Our data showed that, in H-DO, SDF-1 induced callus formation in the gap through the recruitment of BM-ECs/EPCs, the maturation of neo-blood vessels, and increased blood flow. These results indicate that the active recruitment of endogenous BM-ECs/EPCs may provide a substantial clinical benefit for shortening the treatment period of DO.

An experimental study of bone healing around the titanium screw implants in ovariectomized rats: enhancement of bone healing by bone marrow stromal cells transplantation.

PURPOSE: : This study is to evaluate the bone quality of surrounding areas of implants with bone marrow stromal cells (BMSCs) transplantation to rat femur, which have become osteoporosis-induced models. MATERIALS AND METHODS: : The Sprague-Dawley rats were divided into 3 groups: the first group where their ovaries were removed (OVX group), the second group where a sham surgery was given (SHAM group), and the third group where BMSCs were transplanted to an OVX group (OVX-BMSCs group). In the OVX-BMSCs group, 1 × 10 BMSCs were transplanted into femur with implant. Each value of the bone to implant contact and the bone area of each cortical bone and cancellous bone was obtained. Bone density of the width of 500 µm from the implants was measured. RESULTS: : Each ratio of bone to implant contact, bone area, and bone density in the OVX-BMSCs group was significantly higher than those of OVX group as to the cancellous bone. CONCLUSION: : The BMSCs transplantation therapy improved local bone healing in the cancellous bone surrounding implants and also significantly improved bone binding with implants.

Effects of cortical bone perforation on periosteal distraction: an experimental study in the rabbit mandible.

PURPOSE: To investigate tissue reactions using periosteal distraction with decorticating holes in a rabbit model. MATERIALS AND METHODS: Twenty-five Japanese white rabbits weighing 3.2 to 3.7 kg were used. The periosteum was carefully detached, and the buccal cortical bone was porously perforated by drilling in the decortication group. Titanium mesh was placed between the periosteum and the cortical bone, with or without holes. A distraction screw was placed rigidly under the center of the mesh. After a 7-day latency period, the periosteum was distracted 0.5 mm per day for 8 consecutive days. Rabbits were sacrificed after consolidation periods of 4 and 8 weeks. Cross-sectional radiographs were evaluated with densitometry. Specimens were fixed, decalcified, and stained with hematoxylin and eosin. RESULTS: At 8 weeks after periosteal distraction, the area of new bone formation averaged 25.7 +/- 5.1 mm2 and 12.9 +/- 3.2 mm2 (mean +/- SD) with and without decortication, respectively. In this study, periosteal distraction showed better bone regeneration on the lateral aspect of mandibles with rather than without decorticating holes. CONCLUSION: Periosteal distraction with decorticating holes can be effective in augmenting atrophic bone.

Promoted new bone formation in maxillary distraction osteogenesis using a tissue-engineered osteogenic material.

Bilateral maxillary distraction was performed at a higher rate in rabbits to determine whether locally applied tissue-engineered osteogenic material (TEOM) enhances bone regeneration. The material was an injectable gel composed of autologous mesenchymal stem cells, which were cultured then induced to be osteogenic in character, and platelet-rich plasma (PRP). After a 5-day latency period, distraction devices were activated at a rate of 2.0 mm once daily for 4 days. Twelve rabbits were divided into 2 groups. At the end of distraction, the experimental group of rabbits received an injection of TEOM into the distracted tissue on one side, whereas, saline solution was injected into the distracted tissue on the contralateral side as the internal control. An additional control group received an injection of PRP or saline solution into the distracted tissue in the same way as the experimental group. The distraction regenerates were assessed by radiological and histomorphometric analyses. The radiodensity of the distraction gap injected with TEOM was significantly higher than that injected with PRP or saline solution at 2, 3, and 4 weeks postdistraction. The histomorphometric analysis also showed that both new bone zone and bony content in the distraction gap injected with TEOM were significantly increased when compared with PRP or saline solution. Our results demonstrated that the distraction gap injected with TEOM showed significant new bone formation. Therefore, injections of TEOM may be able to compensate for insufficient distraction gaps.